1. Field of the Invention
The present invention relates to an automatic focusing detection device for cameras and more particularly an automatic focusing detection device for cameras capable of dividing an image field into a plurality of sections and of measuring the distances from a camera lens to the subject (subject distances) in each section of the divided field.
2. Related Background Art
A camera capable of dividing an image field into a plurality of sections and measuring the distance each of them is well known in the art as disclosed in Japanese Laid-Open Patent Application Nos. 61-55620 and 62-255921.
In the case of the camera equipped with an automatic focusing detection device of the type disclosed in Laid Open Japanese Patent Application No. 61-55620, an operator operates a switch mounted in the camera in order to select a first mode in which a lens driving motor is controlled based on the results of the distance measurements for plural sections or a second mode in which the lens driving motor is controlled based on the result of the distance measurement for a single focusing detection section corresponding to the center of a frame of a film.
However, in such a case of the conventional camera, a specially designed selection switch must be mounted on the camera. This undesirably reduces the space available for other components.
In the case of the camera disclosed in Laid-Open Japanese Patent Application No. 62-255921, the subject distances for a plurality of sections of the image field are measured by photocells each disposed in opposing relationship with a corresponding section, and the sections which can be focused within the depth of field are measured. Thereafter, a degree of luminance of one or more sections is detected on the assumption that a main subject or object exists within the depth of field. That is, when there is only one section that can be focused within the depth of field, the intensity of a light of this section is measured. When there are more than one such sections, the average of the intensity of light from the sections is used as measured intensity. The above-described camera needs no mechanism for selecting one or more sections whose subject distances must be measured and no mechanism for selecting one or more light measuring sections.
In the above-described system, a section to be focused based on the subject distances of respective sections is determined first and then light of the selected section is measured. However, in spite of the intention of a photographer, there may occur a case in which subject distances are measured not only for a single section which contains a main subject, but for a plurality of sections including the above-mentioned single section. In this case, an exposure value is determined by carrying out the arithmetic operation of the measured light of multiple sections. As a result, when one or more sections have a high degree of luminance as in the case of rear light, it is difficult to photograph a main subject with a correct exposure value. Furthermore, it is also difficult to correctly focus a main subject which a photographer desires to photograph.